To conventionally fabricate, e.g., a gate structure in a manufacturing process of a semiconductor device, a conductor layer [a silicon-containing conductive film layer (e.g., a polysilicon layer, a silicide layer, or a polysilicon layer and a silicide layer deposited thereon)] is formed on an insulating layer of a silicon oxide film layer. Thereafter, the conductor layer is etched into a predetermined pattern through a mask layer formed thereon until the underlying silicon oxide film layer is exposed.
Conventionally, a plasma etching has been widely employed for etching such a silicon-containing conductive film layer formed on the silicon oxide film layer.
When plasma etching the silicon-conductive film layer, the etching is further carried out even after the silicon oxide film layer is exposed, i.e., a so-called overetching is performed, in order to completely remove undesired portions of the silicon-containing conductive film layer from every part on the entire surface of, e.g., a semiconductor wafer.
In such an overetching process, the etching should be applied only to the silicon-containing conductive film layer, not to the exposed silicon oxide film. For this reason, an etching gas for use in the overetching process is required to have a high selectivity of the silicon-containing conductive film against the silicon oxide film (an etching rate of the silicon-containing conductive layer to that of the silicon oxide film). Conventionally, an HBr gas or a mixture gas of HBr and O2 gases has been employed as the etching gas. Further, a pressure during the etching is typically set to be about 0.67 to about 6.7 Pa.
However, circuit patterns of semiconductor devices are getting miniaturized recently. For example, there is a trend for favoring a thinner thickness of the silicon oxide film layer in the above-described gate structure.
Therefore, there is an ever increasing demand for enhancement of a fabrication precision in forming a circuit pattern. In the etching process described above, it is also required to further increase the selectivity of the silicon-containing conductive film layer against the silicon oxide film such that only the desired portions of the silicon-containing conductive film layer can be etched to be removed, without etching the silicon oxide film layer serving as a base layer and without spoiling the etched shape of the silicon-containing conductive film layer.